I've spent much of the year so far working on TMCWv5, with dozens of additional features added, easily enough to offset the "removal" of features which were added to TMCWv4.5 (which can be compared to 1.17 and 1.18, in that 1.17 will implement mostly non-world generation altering features); so far I've added 207 new blocks (including all variants that are obtainable as items), 19 new items, 42 new entities/entity variants, 29 new biomes, and 3 new enchantments.
Of course, I've also made many additions and changes to the underground, including making the largest caves even more extreme, in part as a response to 1.17/1.18; in fact, today I found a cave with a volume of 1.1 million blocks - more than four times larger than the largest cave I found while playing on TMCWv4, and double the size of the largest known cave in that version; this single cave is also nearly as large as an entire giant cave region in TMCWv4, which have also been increased in size from about 1.3 to 1.6 million blocks:
Here are screenshots with coordinates to show just how large the cave is, from end to end and across:
These renderings were made with my CaveFinder utility, with the cave shown by itself below. There is also another huge cave with a volume of over 400,000 blocks just to the north:
Here is a comparison of "special" caves in TMCWv4 and TMCWv5; the latter has more than double the volume of caves, from about 3% to 6.5%, which is well in excess of the average underground volume in vanilla 1.6.4; when including normal caves and mineshafts the volume is about twice as high and the highest of any of my mods in terms of percentage of blocks between lava level and sea level (59 layers vs 52 for vanilla):
Of note, this is the seed "TMCWv4", the same as I played on; the largest cave, ravine, and giant cave region I found are all near the middle of the right edge, with volumes of about 252,000, 267,000 and 1.26 million blocks respectively:
The seed "6511199847387183207" in TMCWv5 (note that this is not final and things may change by the full release); there are many more and on average larger large caves and ravines, as well as many additional variants of caves; a lot of the restrictions on special caves near the origin have also been removed (TMCWv4 has a "no exclusion" patch which disables this, I've considered dropping it for TMCWv5):
Also, this is a graph of the underground volume in most of my mods; TMCWv5 peaks at around 12% while 1.7-1.16 peaks at less than 6%; TMCWv5 only drops that low within 10 blocks of the surface, which itself has about 60% more air blocks (the maps above show caves reaching layer 62 in green but this overestimates surface openings due to the ground generally being deeper than 63 layers):
Also, in the last chart shown above you may notice that the peak in air volume in TMCWv5 compared to lower layers is relatively much greater but I've compensated for that by adding additional ores (gold, diamond, redstone, amethyst) which only generate if they are exposed to air so branch-mining is unaffected and the relative abundances of ores collected while caving is about the same as vanilla 1.6.4, but with about 35% more ores exposed per chunk (this is less than the increase in volume would indicate since it is the surface area that matters); even then, amethyst is still more than a thousand times rarer than coal (given an average of about 2,100 coal mined per play session this gives about 2 amethyst, much of which will be used to repair my gear; in TMCWv4 my pickaxe alone consumed about one per session):
IMO, the move by Mojang to add ores that only generate if they are not exposed is an awful idea that goes completely against a "cave update"; why even bother caving when branch-mining is so much better in just about every way (which is already the case and is one reason why I branch-mine to get resources early on; of course, I made it so that amethyst ore, which has the same initial generation properties as diamond, is 8 times rarer above cave lava level). If easier access to ores in larger caves is a concern it is completely unfounded; I averaged more ores mined per hour in my first world, with vanilla generation, than I did in TMCWv4 (based on very limited experience from a few short runs ores are even easier to collect in 1.8+ due to the generally simpler caves and increased ore generation).
I've also continued to make large-scale refactorings of the vanilla code base; among other things, it is no longer possible to load vanilla worlds as they won't appear in the saves menu, nor can you make a new world with the same name, and statistics are saved separately as well (I previously changed options.txt, which is also thoroughly validated to avoid bugs/crashes caused by invalid settings); of course, it is still imperative to use a custom directory as worlds created with TMCWv5 can still be loaded in vanilla (the damage isn't as severe as you might think since the majority of "blocks" that I've added are variants of existing vanilla blocks. TMCWv5 itself has as much potential to damage vanilla worlds since I've changed many vanilla block IDs; for example, many blocks have been merged into a single ID, such as redstone torches and lamps, wooden stairs, furnaces, and so on, and while many of the freed IDs have been reused some of the blocks, like plants, won't behave well unless they are in a valid location. I've also removed the item forms of many blocks in favor of the block itself being the item; for example, cake now drops itself and is crafted as a block item).
Notably, all of these features have had no noticeable impact on performance or memory usage, as I always see this cited as a reason not to add a suggestion (for example), and mods are otherwise infamous for their resource consumption (I love the claim in this Reddit post that even 1.3, much less 1.6, requires 512 MB to even start up while I see usage typical of 1.2.5, around 256 MB; the only change I made that reduces the impact of the 1.3 client-server merger was to remove spawn chunks, which are only 10-25% of all loaded chunks depending on render distance) - I see no reason for that, as simple calculations would show that the vast majority of memory usage is by loaded chunks, which only depends on the number of blocks loaded, not the number of block types or variants. In fact, despite using only a single thread generating a world with spawn in a Mega Forest biome takes only 2-3 seconds to load the world, making it over 5 times faster than 1.13 (the most recent vanilla version I've run, which implemented multithreaded world generation).
Some of the features I'm adding are also taken from 1.17, such as glow squid, which spawn underground and drop glowstone dust and glow ink sacs which can be used to make glowing item frames (unlike 1.17 they are not a separate entity, you right-click an item frame while holding a (glow) ink sac to apply/remove the effect). I've also added lightning rods, which harmlessly redirect lightning strikes if they are the highest point within a 33x33 area (lightning is a slightly bigger risk than in vanilla since I implemented a change made in vanilla since 1.6.4 where it will seek out entities near the initial strike point and strike them instead; however, it still doesn't turn villagers into witches, which is intentionally not being implemented). Cauldrons can also hold lava, emitting light and burning entities that enter them, and can hold 8 levels of water instead of 3 and put out burning entities and deal damage to endermen, making them a bit more attractive (of course, a water source block still offers infinite water bottle refills).
There are also blocks and items from other vanilla versions, such as composters, which produce dirt instead of bonemeal, making it renewable; I've also considered adding grindstones, which despite being highly controversial can be very useful when enchanting (TMCW still has the pre-1.8 enchantment mechanics, which means spending all your levels for completely unknown enchantments; in particular, while it has an enchantability close to that of gold the rarity of amethyst makes it highly risky to directly enchant, which is part of the reason why I use books. Even if there was a preview I still wouldn't want to risk getting e.g. Fortune/Silk Touch on my pickaxe as it would be impossible to repair if it also had Efficiency V, Unbreaking III, and Mending).
Another notable change is that diamond ender chests, which are a double chest variant of ender chest (total capacity of 3 chests across both) I added in TMCWv2, are now allowed to be picked up with Silk Touch but require end stone to make (more specifically, "diamond end stone", which is made with diamonds and end stone, preserving the original need for diamonds and their name), meaning you can only make them after you've reached the End; this will enable me to use a double-chest ender chest while caving as I did in TMCWv1 (except I also used Fortune back then which negated much of the benefit in terms of longer caving sessions before I ran out of space), which will help when there are more than a dozen variants of iron and gold (I have not made them drop an intermediate item to reduce clutter as it isn't really an issue when I have multiple stacks anyway and smelt them down as needed to make more room; that said, a "Smelting" enchantment I've added makes them drop ingots, which are also affected by Fortune, although it can only be found in chests).
Also, a feature that should be added to vanilla is cave maps, which only map caves that have been lit up by player-placed torches (naturally generated torches are a separate block, which comes in "bright" and "dim" variants, the latter replacing redstone torches which were used in place of normal torches in underground structures so that MCMap wouldn't show unexplored areas; previously, I removed them entirely for this reason, as is still the case in my first world):
This is 3x3 level 0 cave maps (384x384 blocks) covering the giant cave region I explored in TMCWv4:
Yesterday I had just finished a days worth of prismarine farming with my friend lizking10152011 in my Shockbyte server.
He built this igloo on a glacier next to an ocean that is close to an ocean monument, and I made and placed an ender chest in it to give us convenient storage that lets us move our items quicker in bulk.